An ultrasound imaging apparatus, in order to obtain, by means of an ultrasound probe, information on a body part for which a subject requires a diagnosis, transmits ultrasound to this body part.
Additionally, through the ultrasound probe, reflected waves are received from tissue boundaries within the subject, which have different acoustic characteristic impedance values. In this way, the ultrasound imaging apparatus scans ultrasound by means of the ultrasound probe, obtains information on tissues within the subject's body, and converts it into images. Diagnosticians, etc., are able to use these images to perform diagnoses. The ultrasound probe has an ultrasound transducer for the purpose of sending ultrasound waves to the subject, etc., and receiving reflected waves.
In recent years, there have been ultrasound probes that use a rotating or oscillating 1D array ultrasound transducer in the ultrasound probe. Moreover, there have been ultrasound probes based on an electronic scanning method, using a 2D array ultrasound transducer in which ultrasound vibrators (piezoelectric transducers) are disposed in the form of a matrix. Using these ultrasound probes, the study of systems for three-dimensionally acquiring ultrasound images and for displaying them has been progressing. Ultrasound images in 3D are useful in the diagnosis of body parts that are easily overlooked with 2D images. Moreover, with 3D images, it is possible to obtain tomographic images that are suitable for diagnosis or measurement, and an improvement in diagnostic accuracy can be expected.
One example of such an ultrasound probe is one in which an electronic circuit that sends and receives electric signals is embedded within the interior of its handle. The electronic circuit disposed within this ultrasound probe is connected to each of the ultrasound vibrators in the ultrasound transducer. This electronic circuit, based on control signals from the ultrasound imaging apparatus main unit, generates transmission pulses and transmits them to each ultrasound vibrator.
Moreover, this electronic circuit provides batch processing, etc., for electric signals that have been converted by the ultrasound transducer. The electronic circuit transmits the signals that have undergone batch processing to the ultrasound imaging apparatus main unit. In another example of an ultrasound probe, through a switch configured to allow modification of the connection pattern, it is also possible to have a shared connection to a plurality of ultrasound vibrators, as a group. With this configuration, the plurality of ultrasound vibrators is connected as a batch to the transmitting/receiving circuit of the ultrasound imaging apparatus main unit.
One example of the abovementioned conventional ultrasound probe and ultrasound transducer is now explained, using FIG. 1 to FIG. 6. FIG. 1 to FIG. 6 are overview diagrams showing the conventional ultrasound transducer, electronic circuit and the wiring board connecting them, which are provided in an ultrasound probe.
In the ultrasound transducer 300, as shown in FIG. 1, ultrasound vibrators 314 are disposed in a 2D pattern. Moreover, a first acoustic matching layer 310 is disposed adjacently, corresponding to each of the ultrasound vibrators 314. In addition, a second acoustic matching layer 311 is disposed on the surface on the opposite side to the side of the ultrasound vibrators 314 of the first acoustic matching layer 310. In other words, in the ultrasound transducer 300, as shown in FIG. 1, the ultrasound vibrators 314, the first acoustic matching layer 310 and the second acoustic matching layer 311, in that order, are disposed such that they are layered. Moreover, as shown in FIG. 1, for the ultrasound vibrators 314 disposed in a 2D array, on the surfaces on the opposite side to the opposite side to the side of the first acoustic matching layer 310 (hereinafter, “rear surface”), a sound absorbent backing material 318 is provided to the plurality of ultrasound vibrators 314 as a whole.
In this way, in the ultrasound transducer 300, the backing material 318, the ultrasound vibrators 314, the first acoustic matching layer 310 and the second acoustic matching layer 311 are layered in that order, and ultrasound is irradiated in the direction of this layering.
In the ultrasound transducer 300, as shown in FIG. 1, a ground electrode 312 is formed on the surface of the boundary between the ultrasound vibrator 314 and the first acoustic matching layer 310. This boundary surface is hereinafter referred to as the “front surface”.
Moreover, a signal electrode 316 is provided on the surface of the boundary between the ultrasound vibrator 314 and the backing material 318. This boundary surface is hereinafter referred to as the “rear surface”. By making the ground electrode 312 and the signal electrode 316 hetero-polar electrodes, one ultrasound vibrator 314 is sandwiched by electrodes with different polarities, and by electric signals from the electronic circuit, it becomes possible to drive this ultrasonic vibrator 314.
In such a conventional ultrasound transducer 300, as shown in FIG. 2, the ground electrode 312 and the transmitting/receiving circuit are connected via a wiring pattern (not shown in the diagrams) formed on a Flexible Printed Circuit (FPC) 322. Specifically, the first acoustic matching layer 310, which is adjacent to ground electrode 312 of the ultrasound vibrator 314, and the second acoustic matching layer 311 have conductivity. The ground electrode 312 and the wiring pattern of the flexible printed circuit 322 are connected through these, and these wiring patterns are connected in a shared manner, and guided to an electronic circuit.
Meanwhile, in the ultrasound transducer 300, the signal electrode 316 and the transmitting/receiving circuit are, as shown in FIG. 3, connected via the wiring pattern 321 formed on the flexible printed circuit 320. However, with an ultrasound transducer that has a 2D array, the ultrasound vibrators are disposed in a 2D array, so compared with an ultrasound transducer that has a 1D array, the number of ultrasound vibrators increases (for example, by 10 times to 100 times). As a result of this, the number of wiring patterns greatly increases as well.
For example, in the ultrasound transducer 300, as shown in FIG. 3, in order to connect each of the signal electrodes 316 of the ultrasound vibrators 314 with a wiring pattern 321, a connection pad 321a is formed on the flexible printed circuit 320. Hence, on the connection surface with each ultrasound vibrator 314 on the flexible printed circuit 320, for only the number of multiple ultrasound vibrators 314 disposed in a 2D array, connection pads 321a are formed.
However, between the multiple connection pads 321a, additionally, for only the number of ultrasound vibrators 314, wiring patterns 321 must be formed (refer to FIG. 3). With such a configuration, the pitch of the wiring patterns 321 and connection pads 321a is extremely dense, and is extremely difficult to implement.
With the conventional ultrasound transducer 300 shown in FIG. 1 to FIG. 3, the flexible printed circuit 320 is disposed between the backing material 318 and the ultrasound vibrators 314, and a configuration is implemented that makes a connection, by means of the wiring patterns 321, to the transmitting/receiving circuit of the subsequent stage. For this purpose, the entire 2D array of ultrasound vibrators 314 is divided into a plurality of modules, and a flexible printed circuit 320 is provided for each module.
Specifically, as shown in FIG. 4, a plurality of ultrasound vibrators 314 is gathered as one module, in units of a prescribed number, and those modules are disposed in a 2D array, forming the ultrasound transducer 300. By assigning a flexible printed circuit 320 to each module formed from such a group of ultrasound vibrators 314, the number of wiring patterns 321 assigned to each module is reduced.
In this way, it becomes possible to connect the transmitting/receiving circuits 332 and 334 on the relay boards 330 that are disposed corresponding to each module, and the signal electrodes 316.
In this ultrasound transducer 300, as shown in FIG. 4, flexible printed circuits 320 and 322 are interleaved between the modules. For example, between the modules of the ultrasound vibrators 314 shown in FIG. 4, a total of four flexible printed circuits 320 and 322 are provided. Hence, compared to the pitch L1 (FIG. 4) of the ultrasound vibrators 314 within the modules, the pitch L2 of the ultrasound vibrators 314 that are between the adjacent modules becomes longer.
Specifically, the space between the vibrators disposed on the edge of a certain module and the vibrators disposed on the edge of a different, adjacent module will be larger to the extent that the flexible printed circuits 320 and 322 are interleaved between the modules.
However, when the pitch between ultrasound vibrators 314 is large, as in this case, the effect of artifacts due to side lobes increases, and there is a concern that problems will arise with respect to the reliability of the ultrasound images. Additionally, when a plurality of flexible printed circuits 320 and 322 are interleaved between the ultrasound vibrators 314, there is a concern that the precision of the mutual placement of modules will worsen. As a result, there may be a negative effect on the pulse delay control, and the precision of convergence and deflection of the ultrasound beam. Moreover, in the processes for manufacturing the ultrasound transducer, the processes for forming the ultrasound vibrator module will increase, so along with the fact that the manufacturing processes will become more complicated, the cost will increase. Moreover, as a result of the increase in the number of flexible printed circuits 320 and 322, there is a concern that the ultrasound probe may become large in size.
As shown in FIG. 1 to FIG. 3 and in FIG. 4, for this ultrasound transducer 300, an ultrasound transducer that is configured so that electrode leads are embedded in the backing material, and in the backing material, the electrode leads are exposed to the surface on the opposite side to the side in the direction of ultrasound irradiation has been proposed. Regarding such an ultrasound transducer, the configuration of the connections between the electrodes of the ultrasound vibrators and the ultrasound imaging apparatus will now be explained, referring to FIG. 5. FIG. 5 is an overview cross-section diagram showing the configuration of a conventional ultrasound transducer.
With the ultrasound transducer 300 shown in FIG. 5, the needle-shaped electrode leads 325 that are connected to the signal electrodes 316 of the ultrasound vibrators 314 are embedded into the backing material 318. The electrode leads 325 are passed through the inside of the backing material 318 from the boundary surface with the ultrasound vibrators 314 in the backing material 318, and are exposed from the edge surface of the opposite side. Moreover, in this configuration, the electronic circuits 336 are disposed so as to be adjacent to this edge surface of the backing material 318. In addition, the electronic circuits 336 and the tips of the electrode leads 325 that are exposed to the edge surface of the backing material 318 are conductively bonded, and by connecting the electronic circuits 336 with the electrode leads 325, it becomes possible to give conductivity between the signal electrode 316 and the electronic circuits 336.
In the ultrasound transducer 300 shown in FIG. 5, after the signals from the multiple ultrasound vibrators disposed in a 2D array are batch processed by the electronic circuits 336, they are transmitted to the ultrasound imaging apparatus main unit. Hence, with the ultrasound transducer FIG. 5, modules of the ultrasound vibrators 314 are not formed as with the ultrasound transducer in FIG. 4, and it is possible to prevent a situation in which the pitch of the wiring patterns formed on the flexible printed circuits 320 are extremely dense.
However, in the ultrasound transducer 300 shown in FIG. 5, by embedding the electrode leads 325 in the backing material 318, the following problems may arise. Specifically, the backing material 318 is provided for the purpose of acoustic damping of the ultrasound vibrators 314, but embedding electrode leads 325 so as not to cause any effect on the original acoustic characteristics of the backing material 318 is difficult. Moreover, even if this task can be appropriately implemented, the manufacturing processes will be complicated.
Furthermore, there is a need to avoid cross talk between the electrode leads 325. However, the electrode leads 325 are formed at a spacing that is almost the same as that of the array pitch of the ultrasound vibrators 314, so it is difficult to secure spacing between the electrode leads 325 for the purpose of avoiding cross talk.
Additionally, the backing material 318 is configured so as to have a certain length for the purpose of acoustic damping of the ultrasound vibrators 314, but if the length of the electrode leads 325 embedded in the backing material 318 is long, then there is a concern that cross talk may more easily arise. Moreover, the process for processing so as to expose both ends of the electrode lead 325 from each edge surface of the backing material 318 is extremely complicated.
Other than the abovementioned ultrasound transducers shown in FIG. 2, FIG. 4 and FIG. 5, conventionally, ultrasound transducers configured so that the electronic circuits 327 are disposed so as to directly connect with the rear surface of the ultrasound vibrators 314 have been proposed (for example, refer to FIG. 6). As shown in FIG. 6, in this ultrasound transducer 300, the electronic circuits 327 are disposed so as to be adjacent to the rear surface of the signal electrode 316 of the ultrasound vibrators 314. Additionally, the flexible printed circuit 320 is disposed between the electronic circuit 327 and the backing material 318. With this electronic transducer 300, the signal electrode 316 of each ultrasound vibrator 314 is connected to the electronic circuit 327. Hence, the electronic circuit 327 performs processing by batching together many signals. The processed signals are transferred via the flexible printed circuit 320 that is further disposed on the rear surface of the electronic circuit 327. Hence, as shown in FIG. 6, with the ultrasound transducer 300, there is no need to embed the electrode leads in the backing material 318, and immediately beneath the ultrasound vibrators 314, processing is performed to reduce the number of signal paths, so the difficulties associated with circuits with respect to electric signal transmission are eliminated.
The electronic circuit 327 of a conventional ultrasound transducer 300 as shown in FIG. 6 receives signal input from the signal electrode 316 that is connected to the front surface, and outputs signals to the wiring pattern of the flexible printed circuit 320 that is connected to the rear surface. For this purpose, in electronic circuit 327, electrodes become necessary in the front surface and the rear surface. Regarding the ultrasound transducer 300, as a semiconductor process for the purpose of implementing such an electronic circuit 327, there are, for example, TSV (Through Silicon Via) electrodes.
In the ultrasound transducer 300, as shown in FIG. 6, the electronic circuit 327 is disposed between the ultrasound vibrator 314 and the backing material 318. The electronic circuit 327 is configured using a semiconductor material (silicon, etc.). There is a concern that, from the standpoint of acoustic characteristics such as the acoustic characteristic impedance, etc., this semiconductor material may not be compatible with the ultrasound vibrators 314 or the backing material 318, etc. For example, the acoustic characteristic impedance Z of silicon is on the order of 19.5 MRayl. In contrast with this, the acoustic characteristic impedance of ultrasound vibrators 314 made from general PZT-type piezoelectric materials is on the order of 35 MRayl, and there is a large gap between that and silicon. In such cases, the reflectivity at the boundary surface is high, and negative effects from reflected waves may arise. As a result, there is a concern that this may prove disadvantageous for sending and receiving ultrasound with the ultrasound transducer.
Hence, in the ultrasound transducer 300, as shown in FIG. 6, it is necessary, by shortening as much as possible the length in the direction from the front surface of the electronic circuit 327 to its rear surface, and specifically, by minimizing the thickness of the electronic circuit 327 as much as possible, to reduce as much as possible the effects on the acoustic characteristics of the electronic circuit 327 on the sending and receiving of ultrasound, and to avoid a situation that proves disadvantageous for ultrasound imaging.
However, along with reducing the acoustic effects from the electronic circuit 327, the implementation of TSV electrodes connecting the signal electrode 316 with the wiring patterns of the flexible printed circuit 320 is difficult owing to thickness of the electronic circuit 320. Specifically, when the electronic circuit 327 is formed with a thin profile, thus reducing the acoustic effects, it becomes difficult to utilize TSV electrodes, and it is difficult to obtain a connection at both ends of the electronic circuit 327. Conversely, when it is assumed that TSV electrodes will be used in the electronic circuit 327, the thickness of the electronic circuit 327 is increased and there is a concern that due to the acoustic effects, this will prove disadvantageous in the sending and receiving of ultrasound.